Many aromatic alkyl compounds are useful in various fields, and those having a substituent at a para-position are especially important.
The present invention relates to a process for producing with good selectivity a compound having an alkyl group at a para-position of biphenyl.
Among the compounds produced by the process according to the present invention, para-isopropylbiphenyl is useful as a solvent for a dye for pressure-sensitive recording paper, and 4,4'-di-isopropylbiphenyl is convertible to 4,4'-biphenyl dicarboxylic acid or 4,4'-dihydroxybiphenyl by oxidation of side chains.
As a process for producing an alkylbiphenyl, (1) a method of reacting biphenyl with an olefin or an alkyl halide in the presence of a Friedel-Crafts catalyst such as aluminum chloride and (2) a method of reacting biphenyl with an olefin or an alcohol by using a solid acid catalyst such as silica alumina and zeolite are known. These methods, however, have a low selectivity for para-isomers.
Japanese Patent Application Laid-Open (KOKAI) No. 56-156,222 (1981) discloses a method of producing an alkylbiphenyl which is rich in meta- and para-isomers by reacting biphenyl with an olefin while applying silica alumina or zeolite as a catalyst. However, the ratio of para-isomer to meta-isomer in the alkylbiphenyl obtained by this method is not always high enough. This reference does not disclose any process for producing a 4,4'-dialkyl compound.
The following methods are known as a process for producing 4,4'-dialkylbiphenyl.
(1) Synthesis, (11) 822, (1978).
A method of reacting the iodonium salt of diaryl with CH.sub.3 MgS in the presence of NiCl.sub.2 as a catalyst. Since the raw material is difficult to obtain, this method cannot be industrially practicable.
(2) Japanese Patent Publication No. 47-10,705 (1972), U.S. Pat. No. 3,539,622.
A method of producing 4,4'-dialkylbiphenyl from an aromatic mercury compound using CuCl.sub.2, PdCl.sub.2 or LiCl as a catalyst. This reference also discloses a process for producing p,p,-bicumyl (4,4'-di-isopropylbiphenyl). However, a method using a mercury compound is unfavorable in view of influence on a human body.
(3) Azerb. Khim. Zh (1) 21-6 (1971).
A method of producing dialkylbiphenyl by reacting an aromatic halide with metallic sodium is described. This method, however, includes many side reactions such as dehalogenation etc., and the yield of the aimed product is rather low. The use of metallic sodium cannot be an industrial method.
On the other hand, many patents have been presented mainly by Mobil Oil for a process about selective alkylation of an aromatic group by using zeolite. Many of these patents are directed to producing a p-dialkylbenzene and no process to produce an alkylbiphenyl is found except one disclosed in the above Japanese Patent Application Laid-Open (KOKAI) No. 56-156,222 (1981).
Biphenyl derivatives having a substituent at a para-position includes not only p-phenylphenol, 4,4'-dihydroxybiphenyl, which are already under commercial production, but also many useful derivatives such as p-isopropylbiphenyl, p-isopropenylbiphenyl and 4,4'-biphenyl dicarboxylic acid. However, processes for producing these derivatives have not reached a sufficient level, and development of an economical process has been wanted earnestly.
As a result of the extensive studies performed by the present inventors in view of such situation, the present invention has been achieved.